(a) Technical Field
The present invention relates to a nickel-supported catalyst for combined steam and carbon dioxide reforming, more particularly to a nickel-supported catalyst wherein nickel is supported as an active metal on a lanthanum oxide support, as a catalyst which is used in a process of preparing a synthesis gas by combined steam and carbon dioxide reforming with natural gas.
(b) Background Art
A variety of technologies for producing clean fuels are drawing attention due to limitations of fossil fuels and their impact on environmental pollution, Among them, the GTL (gas to liquids) process of preparing a clean synthetic fuel from natural gas is drawing attention. The GTL process consists of a reforming reaction of producing synthesis gas from natural gas and a Fischer-Tropsch synthesis reaction of producing synthetic petroleum from the synthesis gas.
The reforming of methane, which is the principal component of natural gas, can be classified largely into steam reforming of methane (SRM), partial oxidation of methane (POM) using oxygen, carbon dioxide reforming (CDR) of methane, tri-reforming of methane using steam, oxygen and carbon dioxide, etc. The reaction formulas and associated heating values of the reforming reactions are as follows.Steam reforming of methane (SRM): CH4+H2O→CO+3H2, ΔH=208 kJ/mol  {circle around (1)}Partial oxidation of methane (POM): CH4+0.5O2→CO+2H2, ΔH=−38 kJ/mol  {circle around (2)}Carbon dioxide reforming of methane (CDR): CH4+CO2→2CO+2H2, ΔH=247 kJ/mol  {circle around (3)}Tri-reforming of methane (TriR): 3CH4+H2O+0.5O2+CO2→4CO+7H2, ΔH=417 kJ/mol  {circle around (4)}
As can be seen from the above reaction formulas, the molar ratio of carbon monoxide to hydrogen in the produced synthesis gas is different for the reforming reactions. In this regard, diverse research has been carried out on the method of preparing synthesis gases with the H2/CO molar ratio controlled variously from reforming of methane. Among them, combined stream and carbon dioxide reforming (CSCR) of methane using steam and carbon dioxide is drawing a lot of attention.
In combined steam and carbon dioxide reforming (CSCR), the H2/CO molar ratio in the synthesis gas can be controlled variously from 1 to 3 depending on the composition ratio of the reactants. In addition, combined steam and carbon dioxide reforming is advantageous in that the amount of water to be supplied is smaller than steam reforming, the expensive oxygen plant is unnecessary because oxygen is not consumed during reforming, and the durability of catalyst can be increased as compared to carbon dioxide reforming because carbon deposition on the catalyst is slight. Moreover, because the currently available gas fields contain carbon dioxide in large amounts (5-25%), it is environment-friendly in that carbon dioxide is used as a reactant.
For combined steam and carbon dioxide reforming, nickel-based catalysts are mainly used for commercial purposes. Because carbon deposition and sintering of the active component nickel are known as the main cause of the deactivation of the catalyst used in methane reforming, various research has been carried out in order to improve the stability of the catalyst by preventing such phenomena. In this regard, the inventors of the present invention have developed a nickel catalyst for combined steam and carbon dioxide reforming, which exhibits superior resistance to carbon deposition and thermal stability. For example, patent document 1 discloses a nickel-based catalyst wherein a nickel oxide having a perovskite structure is supported on a SiC-Al2O3 support formed of silicon carbide and alumina, patent document 2 discloses a nickel-based catalyst wherein nickel is supported on an η-phase alumina support having many acid sites, and patent document 3 discloses a catalyst wherein an alkaline earth metal is co-precipitated in a catalyst having a hydrotalcite-like structure and containing nickel, magnesium and aluminum. Nevertheless, development of new nickel catalysts capable of resolving the deactivation problem is still needed.